Method and apparatus for compacting earth, sand, gravel, ballast and similar materials

ABSTRACT

In a method of compacting earth, sand, gravel, ballast, etc. by means of a compacting tool, the time-pressure curve representing pressure of the tool on the material being compacted is not sinusoidal but has a shape representing an initial sudden increase in pressure, maintenance of pressure for a selected period of time thereafter and finally a rapid decrease of pressure to a low value. The period during which pressure is maintained after the initial push is long enough to permit the material to become stabilized in a compacted state so that it does not spring back materially when the pressure is released. During the selected period, the pressure can be maintained substantially constant, progressively increased to a higher value, progressively decreased to an intermediate value or quickly decreased to an intermediate value at which it is maintained until the end of the period. Apparatus for carrying out the method comprises a hydraulic cylinder, a fluid pressure system and continuously operating value means controlling the supply of pressure fluid to and discharge of pressure fluid from the hydraulic cylinder to provide the desired nonsinusoidal timepressure curve.

United States Patent 1 Sieke et a1.

[ METHOD AND APPARATUS FOR COMPACTING EARTH, SAND, GRAVEL, BALLAST AND SIMILAR MATERIALS [76] Inventors: Helmut Sieke, An der Trift 5, 3001 Wulferode; Rainer Sieke, Am Pahlberg 18, 3161 Ehlershausen, both of Germany [22] Filed: Mar. 21, 1973 [21] Appl. No.: 343,482

[30] Foreign Application Priority Data Mar. 21, 1972 Germany 2213577 [52] US. Cl. 404/72; 104/10; 404/133 2,043,585 6/1936 Kerwin. 104/12 2084983 6/1937 Baily 404/131 2,254,744 9/1941 Jackson 404/133 2 497.682 2/1950 Mertz l 4 t. 104/12 2,633,782 4/1953 Clement. 404/133 2.821.935 2/1958 Bean 104/12 2,909,106 10/1959 Berrange... 404/133 X $621,786 11/1971 Joy l 104/12 3,625.156 12/1971 Anderson 104/12 3,675,581 7/1972 Plasser et a1. 104/12 FOREIGN PATENTS OR APPLICATIONS 207,874 3/1960 Austria 104/11 1 1 May 27, 1975 12/1960 France 104/10 1/1930 Germany 404/133 [57] ABSTRACT In a method of compacting earth. sand. gravel, ballast, etc. by means of a compacting tool, the time-pressure curve representing pressure of the tool on the material being compacted is not sinusoidal but has a shape representing an initial sudden increase in pressure, maintenance of pressure for a selected period of time thereafter and finally a rapid decrease of pressure to a low value. The period during which pressure is maintained after the initial push is long enough to permit the material to become stabilized in a compacted state so that it does not spring back materially when the pressure is released. During the selected period, the pressure can be maintained substantially constant, progressively increased to a higher value, progressively decreased to an intermediate value or quickly decreased to an intermediate value at which it is maintained until the end of the period. Apparatus for carrying out the method comprises a hydraulic cylinder. a fluid pressure system and continuously operating value means controlling the supply of pressure fluid to and discharge of pressure fluid from the hydraulic cylinder to provide the desired nonsinusoidal time-pressure curve.

9 Claims. 8 Drawing Figures PATENTED M 1915 3,885,883

SHEET 1 F FIGJ FIG.3

METHOD AND APPARATUS FOR COMPACTING EARTH, SAND, GRAVEL, BALLAST AND SIMILAR MATERIALS The present invention relates to a process and apparatus for compacting earth, sand, gravel, ballast and similar materials or mixtures thereof by means of compacting apparatus having a reciprocating compacting tool.

The reciprocation of compacting tools is generally produced mechanically for example by rotating weights or eccentrics which act on the compacting tool. Such reciprocation exhibits a very strong sinusoidal form. Usually weaker vibrations are superimposed on the basic sinusoidal form. Operation of the compacting tool with reciprocation of sinusoidal form has the disadvantage that the material to be compacted is energized sinusoidally which can lead to the effect that the material particles recoil back from their compacted position so that optimal compacting in minimum time is not achieved.

The present invention avoids this difficulty and makes possible optimum compacting of the material in minimum time. In accordance with the invention, the compacting tool at the beginning of a stroke is given a strong push through which high pressure is exerted on the mass to be compacted and after the initial push pressure is maintained for a selected interval of time on the material after which the pressure is relieved.

Thus, in accordance with the invention an intentionally nonsinusoidal oscillation is employed in order first to exert a strong pressure on the mass to be compacted and thereafter to maintain the mass under pressure for a long time so that the forwardly pushed portions of material cannot immediately spring back to another position but are stabilized and held as much as possible in the compacted position. The pressure after the initial push can remain the same or it can increase or decrease as desired.

It has been found advantageous for the compacting work tool to exert pressure in more than one direction.

Moreover, the continuing pressure can act in a direction other than the direction of the initial push. This compacting cycle can be part of another compacting operation.

The objects and advantages of the invention will be more fully understood from the following detailed description in conjunction with the accompanying drawings in which:

FIGS. 1, 2, 3 and 4 are different force-time diagrams in which the coordinate A represents force or pressure applied to the work and the coordinate B represents time;

FIGS. 5, 6 and 7 are schematic illustrations of compacting apparatus for carrying out the method in accordance with the invention; and

FIG. 8 is a schematic view illustrating the use of apparatus in accordance with the invention to compact the ballast of a railway road bed.

FIGS. 1 to 4 illustrate schematically several different waveforms representing the force-time curves of compacting apparatus operating in accordance with the present invention. In these figures the ordinates represent the force or pressure exerted by the compacting tool on the material being compacted while the abscissae represent time. In FIG. 1 there is shown a substantially rectangular waveform which can, for example be obtained with hydraulically driven compacting apparatus. As illustrated in FIG. I, the pressure rises suddenly from an initial low pressure P1 to a high pressure P2. After the peak P2, the pressure drops back slightly to a high pressure P3 at which it is maintained for a selected period of time at the end of which the pressure is suddenly reduced to the initial value Pl.

In FIG. 2 the waveform is trapezoidal and represents progressively increasing force after the initial push. As illustrated in FIG. 2, the pressure rises suddenly from an initial low pressure P1 to a value P2 and then rises progressively at a selected uniform rate to a still higher pressure P3 during a selected period of time at the end of which the pressure drops suddenly back to the initial pressure PI. This can also be obtained with hydraulically driven equipment.

In FIG. 3 the waveform is also trapezoidal but with progressively decreasing force after the initial push. As illustrated in FIG. 3, the pressure rises suddenly from an initial low pressure P1 to a high pressure P2 and then decreases slowly at a selected uniform rate to an intermediate pressure P3 during a selected period of time at the end of which the pressure drops suddenly back to the initial value Pl. This waveform can also be obtained with hydraulically or pneumatically operated equipment.

FIG. 4 illustrates another waveform representing an initial strong push with a lesser pressure exerted thereafter. As illustrated in FIG. 4, the pressure rises suddenly from an initial value PI to a peak high pressure P2 and then drops back quickly to an intermediate value P3 at which it is maintained substantially uniform for a selected period of time at the end of which the pressure drops suddenly back to the initial pressure Pl. This can be obtained mechanically through movement of a rammer which is first catapulted against the material to be compressed and thereafter remains resting on the material for a period of time until it is mechanically withdrawn. It can also be obtained by hydraulically operated apparatus.

In addition to the waveforms illustrated in FIGS. 1 to 4 many other nonsinusoidal waveforms can be generated by different driving means. With these nonsinusoidal waveforms strong compacting can be achieved in an astonishing short time. This leads to optimal results particularly in working on the ballast of railway road beds. Nonsinusoidal waveforms such as those illustrated by way of example in FIGS. 1 to 4 can be generated by suitable mechanical, hydraulic, pneumatic or electro-mechanical equipment. Suitable hydraulically operated means for producing waveforms like those shown in FIGS. 1 to 4 is illustrated schematically in FIGS. 5 to 7.

Hydraulically operated apparatus for producing a time-pressure curve such as that shown in FIG. I is illustrated schematically in FIG. 5. The apparatus is shown as comprising a rotary pressure pump 1 which pumps hydraulic oil under pressure from a storage tank 2 to a rotary control valve 3. From here the hydraulic oil is delivered through a conduit 4 to a working cylinder 5 in which a piston 7 connected with a suitable compacting tool is reciprocable. The piston 7 is movable toward the right as viewed in FIG. 5 by oil pressure in the cylinder 5 and is moved toward the left by a return spring 6. The control valve 3 comprises a casing 3A in which a valve member in the form of a rotor 38 is rotatable and is driven at selected constant speed in the direction indicated by the arrows. for example by a hydraulic or electric motor. The casing 3A is provided with ports communicating respectively with the conduit 4 leading from the control valve to the working cylinder 5, a conduit 4A leading from the pump 1 to the control valve 3 and two oppositely disposed return conduits 10 leading from the control valve 3 back to the storage tank 2. The valve rotor 33 has a diametrically disposed channel 8 for connecting conduit 4A with conduit 4 when the rotor is in proper position to supply pressure fluid from the pump 1 to the working cylinder 5. Further there are two T-shaped channels 9 which are symmetrically disposed and each of which comprises a first channel portion parallel to but spaced from the channel 8 and a second channel portion which is per pendicular to the first channel portion at its midpoint. Each of the T-shaped channels 9 is arranged to connect the conduit 4 from the working cylinder to both of the return conduits 10 when the valve rotor is in proper position. A conduit 48 branching off of the conduit 4 between the control valve 3 and the working cylinder 5 leads to the lower part of a pressure reservoir 11 which comprises a closed vessel divided by a central flexible diaphragm or membrane 11A into an upper chamber containing 2' under pressure and a lower chamber which is connected by the branch conduit 43 to the conduit 4 and is adapted to receive pressure oil from the conduit 4. The gas in the upper chamber of the pressure reservoir 11 is under a pressure of the same order of magnitude as the pressure produced by the pressure pump 1.

The apparatus illustrated in FIG. 5 works in the following manner. The pump l is continuously driven and constantly provides a supply of hydraulic oil under substantially constant high pressure through the conduit 4A to the control valve 3. The rotor 38 of the control valve is rotated continuously in the direction indicated by the arrows. When the central channel 8 of the valve rotor 38 comes into alignment with the ports of the conduits 4 and 4A. pressure fluid flows through the channel 8 and the conduit 4 into the working cylinder 5 and also through conduit 48 into the pressure reservoir 11. The pressure fluid thus supplied to the working cylinder 5 drives the piston 7 which is connected with the compacting tool toward the right as viewed in FIG. 5, thereby compressing the spring 6. Moreover, the diaphragm 11A of the pressure reservoir 11 is deflected upwardly thereby compressing the gas in the upper chamber of the pre ssure reservoir. As soon as the channel 8 of the valve rotor 38 has passed the opening of the conduit 4, the conduit 4 is closed and hence any changes or movements can occur only within the closed system comprising the conduits 4 and 4B, the working cylinder 5 and the pressure reservoir 11. Any such changes or movements are of a relatively limited nature. After the gressure peak upon the introduction of pressure fluid into the system there is only a very slight backward m vement of the piston 7 by the force of the spring 6 upc l equalization of pressure in the sys tem and perhaps tome slight additional flow into the pressure reservoir 11. Thus after the initial pressure peak which occuqs while pressure fluid is supplied to the working cyiinqer 5 by the pump 1, the pressure in the cylinder 5 is m: intained substantially constant since any small losses that may occur are compensated for by the pressure reserioir 11. This pressure is maintained until the valve rotvr 3B has turned approximately 90 to bring the perpendicular stem portion of one of the T-shaped channels 9 into alignment with the port of the conduit 4 whereupon the hydraulic oil is discharged from the working cylinder 5 and the pressure reservoir 11 through both of the return conduits 10 to the storage tank 2. The pressure in the working cylinder 5 is thereupon suddenly reduced so that the piston 7 is moved to the left by the spring 6. When the channel 9 has passed the port of the conduit 4, this conduit is again closed and remains closed during rotating of the valve rotor 38 through another whereupon the channel 8 is again aligned with the ports of conduits 4 and 4A to supply pressure fluid to the working cylinder and the pressure reservoir. It will be seen that two operating cycles of the working cylinder occur during each revolution of the valve rotor 38.

The operating cycle of the apparatus of FIG. 5 is continually repeated through the following phases:

1. Sudden filling of the pressure reservoir 11 and of the working cylinder 5 thereby moving the piston 7 with the compacting tool suddenly toward the right to apply pressure to the material being compacted.

2. The system comprising the working cylinder 5 and pressure reservoir 11 is closed off so that the pressure in the system remains substantially constant and pressure of the compacting tool on the material being compacted is maintained during a selected period of time.

3. The working cylinder 5 and pressure reservoir 11 are connected to the return conduits l0 whereupon pressure fluid is discharged to the storage tank 2. It will be seen that with the channels of the valve rotor disposed as shown in FIG. 5, pressure is maintained in the working cylinder 5 for approximately one half of the cycle of operation. The period during which pressure is maintained can be increased or decreased by moving the stem portion of the T-shaped channel 9 in one direction or the other.

The three phases of a cycle of operation of the apparatus as described above correspond with the timepressure diagram of FIG. 1 in the following manner:

1. An initial sudden rise in pressure with a small overpressure peak.

2. A constant high pressure maintained for a selected period after the initial peak.

3. A sudden decrease of pressure to a lower value. It will thus be seen that the time-pressure curve illustrated in FIG. 1 can be achieved with the apparatus i1- lustrated schematically in FIG. 5.

Apparatus for hydraulically operating a compacting tool in accordance with the time-pressure curve of FIG. 2 is illustrated schematically in FIG. 6. This apparatus likewise comprises a pressure pump 1, an oil storage tank 2, a rotary control valve 3, a conduit 4 leading from the control valve to a hydraulic working cylinder 5 in which a piston 7 is reciprocable and is provided with a return spring 6. However, the rotor 35 of the control valve 3 is different in that a recess 8A is pro vided in the periphery of the rotor at each end of the channel 8 and extends circumferentially from the respective end of the channel 8 in a direction opposite to the direction of rotation of the valve rotor. The circumferential extent of each of the recesses 8A can be se lected as desired but the recesses are shown by way of example in FIG. 6 as extending almost to the discharge channels 9. The discharge channels 9 are also different from those shown in FIG. 5 in that they are L-shaped instead of T-shaped and there is only a single discharge conduit which opens into the valve casing 3A in such position as to communicate with one leg of the channel 9 when the other leg is in registry with the conduit 4 leading from the control valve 3 to the working cylinder 5. The pressure reservoir 11 is also differently arranged in that it is connected by a branch conduit 48 with the conduit 4A leading from the pressure pump 3 to the control valve 3. By reason of these differences in construction, the mode of operation of the apparatus illustrated in FIG. 6 is different from that shown in FIG. 5.

The apparatus shown in FIG. 6 works in the following manner. The pressure pump 1 continually provides a supply of pressure fluid. As long as the channel 8 of the valve rotor 3B is not in alignment with the conduits 4 and 4A the pump 1 supplies pressure fluid only to the pressure reservoir 11. At the instant in which the channel 8 comes into alignment with the ports of the conduits 4 and 4A, a sudden flow ofpressure fluid from the pressure reservoir 11 and from the pressure pump 1 into the working cylinder 5 occurs. Thereby a rapid increase of pressure in the working cylinder 5 occurs and the piston 7 is moved rapidly toward the right thereby compressing the spring 6. When the pressure reservoir II has emptied its contents into the working cylinder 5, the connection between the conduits 4 and 4A is not interrupted because communication is still provided by the recesses 8A. As the pressure pump 1 continues to work, it delivers pressure fluid not only to the pressure reservoir 11 but also to the working cylinder 5. The pressure in the working cylinder 5 is thereby progressively increased. This continues until the valve rotor 38 has rotated so that the recesses 8A are no longer in communication with the conduits 4 and 4A. At this instant the increase in pressure ceases. However, shortly thereafter a connection is established by the channel 9 between the conduit 4 leading to the working cylinder 5 and the discharge conduit 10 so that pressure fluid is discharged out of the working cylinder 5 through the conduit 4, channel 9 and conduit 10 into the storage tank 2. The pressure in the working cylinder 5 thereby decreases to a low value. The piston 7 is thereby unloaded and is moved toward the left by the return spring 6.

The cycle of operations of the apparatus shown in FIG. 6 during continuous rotation of the rotor 38 of the control valve 3 is as follows, it being understood that there are two cycles of operation of the hydraulic cylinder and piston for each complete rotation of the valve rotor.

l. Sudden filling of the working cylinder 5 from the previously filled pressure reservoir 11 and from the pressure pump 1 thereby applying pressure to the piston 7 and moving the piston suddenly to the right to apply pressure through the compacting tool to the material being compacted.

2. The pressure pump operates after emptying of the pressure reservoir to supply pressure fluid to the working cylinder and to the pressure reservoir, thereby producing a progressively increasing pressure in the working cylinder during a selected period of time.

3. Sudden emptying of the working cylinder through flow of pressure fluid through the return conduit to the storage tank 2. This mode of operation corresponds to the time-pressure curve shown by way of example in FIG. 2 as follows:

1. Sudden increase of pressure;

2. Slow and progressive further increase of pressure during a selected period of time;

3. Sudden decrease of pressure to a low value. It will be understood that the period of time during which pressure is progressively increased depends on the circurnferential extent of the recesses 8A of the valve rotor 33. As shown by way of example in FIG. 6 the recesses 8A have a circumferential extent of almost so that the period during which the pressure progressively increases as shown in FIG. 2 extends for approximately one half of a full cycle. The period can be decreased by decreasing the circumferential extent of the recesses 8A so that the pressure would be progressively increased until the ends of the recesses 8A reach the ports of conduits 4 and 4A whereupon the conduit 4 would be closed so as to maintain substantially constant pressure in the cylinder 5 until the discharge channel 9 of the valve rotor reaches the port of the conduit 4. Alternatively, by changing the positions of the discharge channels 9, the circumferential extent of the recesses 8A can be increased so as to lengthen the period of time that pressure in the working cylinder 5 is progressively increased.

In FIG. 7 there is shown a further embodiment of the apparatus suitable for realizing the time pressure curve of the kind shown in FIG. 3. Also here there is a pressure pump 1, a storage tank 2, a control valve 3, a working cylinder 5 connected with the control valve by a conduit 4 and a piston 7 reciprocable in the cylinder and biased in one direction by a spring 6. There is also a return conduit 10 and a pressure reservoir 11. Differences reside in the form of the rotor 3B of the control valve 3 and in the connection of the pressure reservoir 11 with the control valve. The pressure reservoir 11 is connected with a separate port provided in the casing 3A of the control valve slightly in advance of the port of the conduit 4 connecting the control valve with the working cylinder 5 and in position to be in the path of movement of the channels 8 and 9. Moreover, the conduit 4B connecting the pressure reservoir 11 with the control valve is provided with a valve 12 which throttles flow of liquid into the reservoir but permits quick emptying of the reservoir. The valve 12 can for example comprise a conical chamber comprising a ball which is movable toward the narrow end of the chamber by flow of oil in a direction toward the pressure reservoir so as to restrict the flow while being movable toward the larger end of the chamber by flow of oil in the opposite direction so that oil can flow out of the pressure reservoir rapidly.

As in the previously described embodiments the rotor 38 of the control valve 3 is provided with a diametrically disposed channel 8 which connects the pressure pump 1 with the working cylinder 5 when it is aligned with the ports of the conduits 4 and 4A. Moreover, there are two L-shaped channels 9 for connection with the return conduit 10. The rotor of the valve 3 is further provided with opposite circumferentially ex tending recesses B which are disposed between respective ends of the channels 8 and 9 and serve to provide a connection between the conduit 4 leading to the working cylinder 5 and the conduit 48 leading to the pressure reservoir 11. These recesses are not connected either with channel 8 or with the channels 9. Furthermore. the port of the valve casing connected with the return conduit 10 is enlarged by a recess C which extends circumferentially in a direction opposite to the direction of rotation of the valve rotor a distance corresponding approximately to the spacing of the valve ports for the conduits 4 and 4B respectively.

The apparatus illustrated in FIG. 7 works as follows. The pump 1 is operated continuously to supply oil pressure and the rotor 38 of the control valve is continu' ously rotated in the direction indicated by the arrows. When the channel 8 of the valve rotor comes into alignment with the ports of conduits 4 and 4A, pressure fluid from the pump 1 flows rapidly through conduit 4A, channel 8 and conduit 4 to the working cylinder 5 thereby producing a sudden increase in pressure in the working cylinder and moving the piston 7 to the right thereby compressing the spring 6. Soon after the channel 8 passes the port of the conduit 4, the recess 8 of the valve rotor comes into communication with the conduit 4 thereby connecting the working cylinder 5 with the pressure reservoir 11 through the conduit 4, recess B and conduit 48. The pressure fluid can thereby flow from the cylinder 5 to the pressure reservoir 11. However, flow is restricted by the valve 12 so that there is only a gradual and progressive decrease of pressure in the cylinder 5. This continues until the trailing end of the recess B passes the port of the conduit 48. Shortly thereafter the return channel 9 of the valve rotor comes into communication with the port of the conduit 43 so that pressure fluid is discharged from the pressure reservoir to conduit 48, channel 9 and conduit to the storage tank 2. When the return channel 9 reaches the port of conduit 4, pressure fluid remaining in the cylinder 5 is discharged rapidly through the con duit 4, channel 9 and conduit 10 thereby producing a sudden drop in pressure to a low value. The enlarge ment of the port of conduit 10 by the circumferentially extending recess C provides for communication of the channel 9 with the conduit 10 when the channel 9 is in communication with the port of the conduit 48 as well as with the port of the conduit 4. Upon the sudden decrease of pressure in the working cylinder 5 the piston 7 is returned to the left by the spring 6.

Continuous rotation of the rotor of the control valve 3 of the apparatus of FIG. 7 produces the following phases in the cycle of operations:

1. Rapid filling of the working cylinder 5 with a sudden increase in pressure to a high value thereby forcing the piston 7 rapidly to the right and applying pressure through the compacting tool to the material being compacted.

2. A progressive and partial decrease in pressure in the working cylinder during a selected period of time after the initial sudden increase in pressure.

3. Final sudden decrease in pressure in the working cylinder to a low value whereupon the piston 7 is returned 0 the left by the spring 6. This operation of the apparatus produces the time-pressure curve shown in FIG. 3 having the following characteristics.

1. Sudden initial rise of pressure in the working cylinder.

2. Progressive straight line decrease of pressure in the working cylinder during a selected period of time after the initial sudden increase.

3. Sudden decrease of pressure in the working cylinder to a low value.

It will be understood that in contrast with a sinusoidal waveform in accordance with which the rate of decrease in pressure is continually changing, the rate of decrease of pressure with the apparatus and method of the present invention as illustrated in FIGS. 3 and 7 is substantially constant so that the progressive decrease in pressure is represented by a straight line. The rate of decrease of pressure and hence the slope of the line are controlled by the throttling valve 12 which regulates flow of pressure fluid from the working cylinder 5 to the pressure reservoir 11 during the time that the recess B of the valve rotor is in communication with the ports of conduits 4 and 4B. The rate of decrease can thus be increased or decreased by decreasing or increasing the resistance provided by the throttling valve 12. The length of the period during which pressure in the working cylinder is progressively decreased after the initial sudden increase is controlled by the length of the recess B in the rotor 3B of the control valve. Thus, within the limits of design of the valve this period can be increased or decreased. If the recess B is made shorter at its lead ing end, pressure in the cylinder 5 will be maintained at a substantially constant value for a period of time following the sudden pressure increase and thereafter will decrease progressively during the time that the recess B provides communication between conduits 4 and 48. If the recess B is shortened at its trailing end the pressure time curve will have a substantially horizontal portion following the downward slope and prior to the finaal sudden decrease in pressure.

It should be mentioned that in the apparatus shown schematically in FIGS. 5 to 7, pressure pumps of different capacities can be used and that the pressure reservoirs 11 can also be of different sizes according to the bore and stroke of the working cylinder 5, the volumetric capacity and pressure characteristics of the pump and the desired operating characterstics of the apparatus.

The time-pressure curve shown in FIG. 4 can also be obtained with apparatus such as that illustrated in FIG. 7 by omitting the throttling valve 12 in the conduit 48 between the control valve 3 and the pressure reservoir 11. With this modification, pressure in the working cylinder rises rapidly as previously described when the channel 8 of the control valve provides communication between conduits 4A and 4. When the recess B of the control valve rotor comes into communication with the ports of conduits 4 and 4B, pressure fluid flows rapidly from the working cylinder 5 to the pressure reservoir 11 until pressure in the closed system comprising the cylinder 5, conduits 4 and 4B and the pressure reservoir 11 is equalized. This results in a sudden drop of pressure in the cylinder 5 to a level intermediate minimum and maximum pressures in the working cylinder. The level to which the pressure drops can be controlled by varying the respective capacities of the pressure reservoir 11 and the working cylinder 5. If the pressure reservoir is made smaller, the pressure drop will be less and conversely a larger pressure drop results from the provision of a larger pressure reservoir. When the return channel 9 reaches the port of conduit 4B, pressure fluid is discharged from the pressure reservoir 1 1, which is no longer in communication with the working cylinder 5. When the return channel 9 reaches the port of conduit 4, pressure fluid is rapidly discharged from the working cylinder 5 through conduit 4, channel 9 and conduit 10 to the storage tank 2 thereby producing a final decrease of pressure to a low value. The timepressure curve illustrated in FIG. 4 is thereby procluced.

It will be seen that in all of the illustrated embodiments, pressure is maintained by the compacting tool on the material being compacted during a selected period of time after the initial sudden application of high pressure. During this period of time the pressure may be maintained approximately constant as illustrated in FIG. 1, may progressively increase as illustrated in FIG. 2, may progressively decrease to an intermediate value as illustrated in FIG. 3 or, as is illustrated in FIG. 4, it may drop quickly to an intermediate value which is maintained throughout the selected period. Through suitable design of the control valve as described above, the length of the period of time during which pressure is maintained can be varied as desired. To obtain the desired results, the period of time during which pressure is maintained should be long enough to permit the material being compacted to stabilize in its compacted state so that it will not bounce back after release of pressure. Preferably the period of time during which pressure is maintained is at least one quarter of a complete cycle of operation of the compacting tool. In the embodiments illustrated by way of example in the drawings, the period is equal to approximately one half of the working cycle.

FIG. 8 shows schematically a practical application of the apparatus shown by way of example in FIGS. 5 to 7. In FIG. 8 compacting tools 13 are shown compacting the ballast bed 14 supporting the ties l5 and rails 16 of a railway line. The compacting tools 13 have working ends of stepped pyramid form and are shown as being operated to compact the ballast underneath the ties. For this purpose the compacting tool is actuated by two hydraulic cylinders such as are illustrated in FIGS. 5 to 7, one of the cylinders being arranged to move the compacting tool vertically and the other being arranged to move it horizontally. The rotors of the control valves of the respective hydraulic cylinders are out of phase relative to one another, for example by 45, so that after the compacting tool has been moved downwardly by one cylinder and while it is still held in pressure contact with the ballast, the tool is moved horizontally by the other hydraulic cylinder. In this manner effective tamping of the ballast underneath the ties can be effected in a very short time. If desired the rotors of both control valves can be arranged on the same shaft so as to maintain the selected phase relation between them. It will be seen that by reason of the size and shape of the tool and its mode of actuation a selected small area of the ballast is subjected to a periodic succession of individual pressure thrusts by the compacting tool which reciprocates periodically but in a nonsinusoidal manner so as to maintain pressure on the material for a selected period of time after each pressure thrust. The effectiveness of the compacting tool is thereby greatly increased.

While in FIGS. 5 to 8 there is illustrated apparatus suitable for carrying out the method herein described and illustrated in FIGS. 1 to 4, it will be understood that other apparatus operated for example hydraulically, pneumatically, mechanically or electro-mechanically may be used if desired. Moreover, modifications can be made in the apparatus illustrated in FIGS. 5 to 8 while still maintaining essentially the same mode of operatron.

What we claim and desire to secure by letters patent is:

LII

1. A process for compacting earth, sand, gravel, ballast and similar material which comprises subjecting a selected small area of sand material at a time to a periodic succession of individual pressure thrusts by means of a rectilinearly reciprocating compacting tool which is reciprocated cyclically but non-sinusoidally, the compacting tool at the beginning of each cycle being given a strong push through which a strong compacting pressure thrust is exerted on said material and pressure being thereafter maintained on said material by said tool for a selected period of time not less than one quarter of a cycle to hold the compacted material in place and thereby allow time for it to become settled and fixed in compacted condition, whereupon the pressure of said compacting tool on said material is relieved to complete the cycle, and thereupon repeating the cycle.

2. A process according to claim 1, in which the pressure exerted by said compacting tool on said material is maintained substantially constant for a selected period of time after an initial push.

3. A process according to claim 1, in which the pressure exerted by said compacting tool on said material is progressively increased during a selected period of time after an initial push.

4. A process according to claim 1, in which the pressure exerted by said compacting tool on said material progressively decreases during a selected period of time after an initial push.

5. A process according to claim 1, in which said compacting tool is given a rectilinear compacting movement in a first direction to exert a compacting action on said material and thereupon in the same cycle is given a further rectilinear compacting movement in a second direction approximately at right angles to said first direction.

6. A process for compacting earth, sand, gravel, ballast and like material which comprises subjecting a selected small area of said material to a periodic succes sion of individual pressure thrusts by a compacting tool reciprocated rectilinearly cyclically but nonsinusoidally by a hydraulic cylinder, said process comprising providing a continuous supply of hydraulic fluid under predetermined pressure for operating said hydraulic cylinder and cyclically controlling the supply of said pressurized hydraulic fluid to and discharge of said fluid from said cylinder to actuate said compacting tool, each cycle comprising:

a. supplying pressurized fluid rapidly to said hydraulic cylinder to move said compactng tool suddenly in a direction toward said material to subject the small area of said material engaged by said tool to a strong compacting pressure thrust,

b. thereupon maintaining pressure in said hydraulic cylinder and thereby maintaining pressure of said compacting tool on the compacted material for a selected period of time not less than one quarter of a cycle to hold the compacted material in place and thereby allow time for it to become settled and fixed in compacted condition, and

c. thereafter permitting discharge of said fluid from the hydraulic cylinder and applying a force to retract said compacting tool, whereby the pressure of said compacting tool on said material is momentarily relieved.

7. A process according to claim 6, in which said selected period that pressure is maintained in said hybeing supplied to said second hydraulic cylinder to effect said movement in said second direction and the supply oipressurized hydraulic fluid to said second cylinder being controlled in timed relation to the supply of pressurized hydraulic fluid to said first mentioned hydraulic cylinder to effect said movement of said compacting tool in said second direction after said compacting thrust and while pressure is maintained in said first mentioned hydraulic cylinder. 

1. A process for compacting earth, sand, gravel, ballast and similar material which comprises subjecting a selected small area of sand material at a time to a periodic succession of individual pressure thrusts by means of a rectilinearly reciprocating compacting tool which is reciprocated cyclically but nonsinusoidally, the compacting tool at the beginning of each cycle being given a strong push through which a strong compacting pressure thrust is exerted on said material and pressure being thereafter maintained on said material by said tool for a selected period of time not less than one quarter of a cycle to hold the compacted material in place and thereby allow time for it to become settled and fixed in compacted condition, whereupon the pressure of said compacting tool on said material is relieved to complete the cycle, and thereupon repeating the cycle.
 2. A process according to claim 1, in which the pressure exerted by said compacting tool on said material is maintained substantially constant for a selected period of time after an initial push.
 3. A process according to claim 1, in which the pressure exerted by said compacting tool on said material is progressively increased during a selected period of time after an initial push.
 4. A process according to claim 1, in which the pressure exerted by said compacting tool on said material progressively decreases during a selected period of time after an initial push.
 5. A process according to claim 1, in which said compacting tool is given a rectilinear compacting movement in a first direction to exert a compacting action on said material and thereupon in the same cycle is given a further rectilinear compacting movement in a second direction approximately at right angles to said first direction.
 6. A process for compacting earth, sand, gravel, ballast and like material which comprises subjecting a selected small area of said material to a periodic succession of individual pressure thrusts by a compacting tool reciprocated rectilinearly cyclically but non-sinusoidally by a hydraulic cylinder, said process comprising providing a continuous supply of hydraulic fluid under predetermined pressure for operating said hydraulic cylinder and cyclically controlling the supply of said pressurized hydraulic fluid to and discharge of said fluid from said cylinder to actuate said compacting tool, each cyCle comprising: a. supplying pressurized fluid rapidly to said hydraulic cylinder to move said compactng tool suddenly in a direction toward said material to subject the small area of said material engaged by said tool to a strong compacting pressure thrust, b. thereupon maintaining pressure in said hydraulic cylinder and thereby maintaining pressure of said compacting tool on the compacted material for a selected period of time not less than one quarter of a cycle to hold the compacted material in place and thereby allow time for it to become settled and fixed in compacted condition, and c. thereafter permitting discharge of said fluid from the hydraulic cylinder and applying a force to retract said compacting tool, whereby the pressure of said compacting tool on said material is momentarily relieved.
 7. A process according to claim 6, in which said selected period that pressure is maintained in said hydraulic cylinder is approximately one half of each cycle.
 8. A process according to claim 6, in which said pressure in said hydraulic cylinder is maintained substantially constant for said selected period of time.
 9. A process according to claim 6, in which after said compacting thrust, said compacting tool is moved rectilinearly in a second direction approximately at right angles to the direction of said compacting thrust by a second hydraulic cylinder, pressurized hydraulic fluid being supplied to said second hydraulic cylinder to effect said movement in said second direction and the supply of pressurized hydraulic fluid to said second cylinder being controlled in timed relation to the supply of pressurized hydraulic fluid to said first mentioned hydraulic cylinder to effect said movement of said compacting tool in said second direction after said compacting thrust and while pressure is maintained in said first mentioned hydraulic cylinder. 